Hydraulically driven cryogenic refrigerator



Sept. 29, 1970 m A. G. OBI-IN: I 3,530,681

HYDRAULICALLY DRIVEN CRYOGENIC REFRIGERATOR Filed Aug. 5, 1968 Hill! I!"Axel G. Dehne,

INVENTOR BY. CZwM ATTORNEY.

United States Patent 3,530,681 HYDRAULICALLY DRIVEN CRYOGENICREFRIGERATOR Axel G. Delme, Los Angeles, Calif., assignor to HughesAircraft Company, Culver City, Calif., a corporation of Delaware FiledAug. 5, 1968, Ser. No. 750,163 Int. Cl. F25b 9/00 U.S. Cl. 62-6 13Claims ABSTRACT OF THE DISCLOSURE This disclosure specifically relatesto an arrangement wherein cryogenic refrigerator expander and compressorpistons are actuated back and forth under the influence of refrigerantpressure and hydraulic pressure. Continuation of the refrigerant isavoided by providing bellows to hermetically seal the pistons withinrespective interconnected refrigerator subchambers. Each piston iscontrolled by a valve assembly having a two-position valve to allowrefrigerant gas pressure to move the respective piston in a firstdirection when the valve is in a first position and to allow hydraulicpressure to move the respective piston in a second direction when thevalve is in a second position. These valves are shifted betweenpositions at appropriate times in the refrigeration cycle by hydraulicsignals traveling through hydraulic passages including portionspositioned within the pistons so that the pistons may reciprocate 90 outof phase.

This invention relates to a fluid drive unit for operating cryogenicrefrigerators or other devices. The invention further relates to ahydraulic drive unit for reciprocating a plurality of pistons in phasedsynchonous relationship. More particularly, the invention relates to anarrangement wherein a hydraulic drive unit is utilized for reciprocatingthe pistons of a cryogenic refrigerator.

As is Well known, cryogenic refrigerators utilizing the Stirling andother cycles, employ, in the transfer of a gas between a compressioncylinder and an expansion cylinder, a regenerating device through whicha compressible refrigerant gas is passed and which characteristical lyabsorbs heat from the refrigerant as it moves to the expansion chamber,delivering gas thereto at a relatively low temperature. On the returnphase of the cycle, the relatively cold refrigerant again passes throughthe regenerator, absorbing heat stored therein so that the refrigerantis delivered to the compression chamber at a realtively hightemperature.

Cryogenic refrigerators of the prior art operating in this manner haveconventionally employed electric motors producing a rotary motion andcrank and rod mechanisms for converting the rotary motion intosynchronous- 1y phased reciprocation of the compressor and expanderpistons. Such an arrangement gives rise to problems. For example, thistype of arrangement requires bearings and lubricants, and the lubricantstend to contaminate the refrigerant. More importantly, such arrangementsare relatively noisy due to piston slapping, and side loads on the sealsof the cryogenic refrigerator limit the useful life of the refrigerator.Further, and most significantly, the utility of such arrangements issomewhat restricted due to vibration thereof during operation.Operational vibrations are generally undesirable in mechanical devicesand, with reference to cryogenic refrigerators which may be used inconjunction with vibration sensitive equipment or optical devices, suchvibrations should be minimized as much as possible. Generally, whenrotating mechanisms are used to drive a crank and rod arrangement,counter weights are rigidly placed on the crank in such a position as toreduce vibration. Also, it is common to dynamically balance the movingpistons of such prior art devices against vibration by operating twosuch devices, suitably arranged within a common housing, in opposeddirections. In the first instance detrimental vibrations can not becompletely avoided, while, in the second instance, detrimentalvibrations can be completely avoided but at the expense of a duplicatemechanism.

It is, therefore, a primary object of the invention to provide ahydraulic drive unit for a plurality of pistons.

It is another object of the invention to provide a hydraulic drive unitfor a cryogenic refrigerator wherein hydraulic fluid pressure isoperable to reciprocate an expander and compressor piston in phasedsynchronous relationship whereby relatively noise-free long-lifeoperation is obtainable.

It is another object of the invention to provide a cryogenicrefrigerator which, in operation, is capable of approximating a Stirlingcycle.

It is another object of the invention to provide an arrangement whereinthe refrigerant of a cryogenic refrigerator is permanently sealed toavoid contamination by lubricants.

It is another object of the invention to provide an arrangement forreciprocating the pistons of a cryogenic refrigerator which can bereadily dynamically balanced, due to the elimination of the conventionalcrank and rod, by the provision of opposite stroking weights toessentially eliminate vibrations during operation thereof.

These and other objects are accomplished in accordance with theinvention by operating an expander piston and a compressor piston inout-of-phase synchronous relationship. The pistons respectivelyreciprocate in an expander cylinder and a compressor cylinder which areinterconnected and which contain a compressible refrigerant gas such ashelium or the like under pressure. These pistons are moved back andforth in the respective chambers by refrigerant pressure and hydraulicpressure by controlled application of fiiud pressure to the pistons bymeans of suitable hydraulic valving. The valving includes a two-positionvalve for each piston to allow refrigerant pressure to move therespective piston in a first direction when the valve is in a firstposition and to allow hydraulic pressure to move the respective pistonin a second direction when the valve is in a second position. Thesevalves are shifted between positions at appropriate times in therefrigeration cycle by hydraulic signals traveling through hydraulicpassages including portions positioned within the pistons so that thepistons are caused to reciprocate out of phase.

These and other features and advantages of the invention can be moreclearly understood by reference to the following specification and therelated drawing wherein a preferred embodiment incorporating theinvention is shown. In the drawing certain parts are shown in crosssection to facilitate an understanding of the invention.

Describing the arrangement in detail and directing attention to thefigure, it will be seen that the cryogenic refrigerator 10 for coolingload 11 comprises a hermetically sealed chamber in a housing. Coolingload 11 may be any device such as an infrared detector or parametricamplifier which must be maintained at cryogenic temperatures. Thehousing chamber is comprised of an expander subchamber 12 and acompressor subchamber 13 interconnected by a passage 14. The wall ofrefrigerator 10 in the vicinity of expander subchamber 12 is extremelythin to limit flow of heat by conduction to subchamber 12 thusincreasing the efficiency of refrigerator 10. EX- pander piston 15 andcompressor piston 16 have respective piston heads or displacers 17 and18. Disposed within a peripheral groove within each piston head is an O-ring and continuous annular Teflon rider, 17a and 18a respectively,which effectively serve as seals and which may not be necessary in agiven embodiment. Obviously, a skilled workman can design the pistons,and so forth, so as to obtain various piston compression ratios asdeemed expedient. Respective resilient members such as bellows 19 and 20are welded or otherwise suitably attached to peripheral portions ofpiston heads 17 and 18, and to the walls of the housing so as tohermetically seal cryogenic refrigerator 10. The chamber of cryogenicrefrigerator is filled with a compressible refrigerant gas such ashelium or the like under a relatively high pressure.

Expander piston has conventional regenerator means 21, such as a onestage regenerator, through which refrigerant gas may pass back andforth. Exemplarily, regenerator means 21 may comprise stacked stainlesssteel screens, glass beads, lead balls, or the like, whichcharacteristically have a suitable thermal capacity characteristic and arelatively high surface area to volume ratio.

The expander piston 15 is provided with peripheral grooves in whichO-rings 22 and 23 are disposed. These O-rings are operative to expandrespective seals (not shown), such as Teflon riders, of generallyannular configuration having an L-shaped cross section, against the wallof the piston cylinder to prevent or minimize leakage of refrigerant gasback and forth between expander subchamber 12 and expander bellowchamber 24. Expander passages 25 and 26 provide communication betweenexpander subchamber 12 and compressor subchamber 13 via regenerator 21which is mounted within an enlarged chamber in the expander pistonportion or displacer 27. Passage 26 is so arranged as to provide theaforementioned communication regardless of the position of expanderpiston 15.

In order to provide for synchronous reciprocation of pistons 15 and 16 ahydraulic drive unit 28 is provided. Unit 28 comprises hydraulic drivevalve assemblies 29 and 30. In valve assembly 29, a movable valve spool31 is disposed within portion 321: of hydraulic reservoir 32. Spool 31and portion 32a are complementarily shaped so that spool 31 is snuglyfitted within portion 32a, and portion 32:: is of sufficient length toallow spool 31 to slide back and forth therein. Portion 32b of reservoir32 is dimensioned for a snug slide fit with the corresponding portion ofpiston 15.

In the embodiment shown, spool 31 is cylindrical, but it may be of anysuitable shape. Spool 31 has transverse spaced holes or openings 33 and34 drilled therethrough and so located that when valve spool 31 is in afirst position opening 33 is aligned with valve port 35 and when valvespool 31 is in a second position, opening 34 is aligned with valve port36. In lieu of openings 33 and 34 peripheral grooves may be cut intospool 31 to serve the same purpose.

In hydraulic valve assembly 30, it can be seen that movable valve spool37, hydraulic reservoir 38, reservoir portions 38a and 38b, spoolopenings 39 and 40, and valve ports 41 and 42 are arranged in a fashionsimilar to the arrangement of the comparable elements of hydraulic valveassembly 29. Hydraulic pump P is connected to port 35 and hydraulic pumpP is connected to port 41. Port 36 is connected to vent line V and port42 is connected to vent line V Hydraulic conduit means operably connecthydraulic pump P to valve spools 31 and 37 whereby these spools may bemoved back and forth to control the application of hydraulic fluidpressure to the faces 41 and 42 of the respective expander piston 15 andcompressor piston 16. Hydraulic fluid passages 43, 44, 45, 46, 47 and 48are arranged so that, when expander piston 15 is at the bottom of itsstroke, fluid pressure from hydraulic pump P will actuate valve spool 31to bring valve spool opening 33 into alignment with valve port 35.Hydraulic fluid passages 49, 50, 51 and 52 are arranged so that, shortlyafter expander piston 15 has completed one half of its upward stroke,hydraulic pump P will actuate valve spool 37 to align valve spoolopening 39 with valve port 41. Hydraulic fluid passages 46 and 53 arearranged so that, when expander piston 15 has completed its upwardstroke, a hydraulic path is completed between hydraulic pump P and ventline V whereby valve spool 31 is actuated so as to bring valve spoolopening 34 into alignment with valve port 36. Hydraulic fluid passages50 and 49 are arranged so that, when compressor piston 16 has reachedthe top of its upward stroke, a hydraulic fluid path is completedbetween hydraulic pump P and vent line V whereby valve spool 37 isactuated to bring valve spool opening 40 into alignment with valve port42. Finally, O-rings 54 and 55, together with respective seals (notshown) of the same type as those used in conjunction with previouslymentioned O-rings 22 and 23, are respectively disposed in peripheralgrooves adjacent respective pistons 15 and 16 and seal the housing ofhydraulic unit 28 to prevent or minimize leakage of hydraulic fluidtherefrom.

In operation, assuming pistons 15 and 16 are in the position shown,piston 15 has completed slightly more than half of its upward stroke,piston 15 being driven upward by the force of hydraulic pressure uponpiston face 41 exerted by hydraulic pump P At this time, piston face 41has cleared passage 49 while passage 51 of piston 16 interconnectspassages 50 and 52 whereby a hydraulic fluid path is completed betweenpump P and vent line V and valve spool 37 is moved to align opening 39with valve port 41. Hydraulic pressure for pump P now exerts a hydraulicforce upon piston face 42 to drive compressor piston 16 upwardly. Bothpistons 15 and 16 now travel concurrently upward, with expander piston15 leading compressor piston 16 by approximately thereby compressing therefrigerant gas in the cryogenic refrigerator 10 to decrease the volumeand increase the pressure thereof. During this initial phase of thecycle the heat of compression which is generated is rejected to theambient through the walls of the housing, as indicated by Q so that thisphase is relatively isothermal.

Expander piston 15 now reaches its top positio whereupon hydraulic fluidpassages 46, 45, 53 and 48 complete a hydraulic fluid path between pumpP and vent line V thus shifting valve spool 31 to bring valve spoolopening 34 into alignment with valve port 36. The refrigerant gaspressure of the refrigerant gas in the interconnected subchambers 12 and13 and in the bellow chambers 24 is now operative to push expanderpiston 15 downward expelling hydraulic fluid from hydraulic reservoir 32through port 36 to vent line V The extent to which the refrigerant gasin the bellow chamber 24 pushes the expander piston 15 downward inrelation to the extent to which the refrigerant gas in theinterconnected subchambers 12 and 13 pushes the expander piston 15downward depends upon the design of the pistons 15 and 16, and so forth,as indicated earlier herein.

During the initial portion of this downward stroke of expander piston15, compressor piston 16 continues upward and the arrangement preferablyis such that the total volume of the refrigerator chamber remainssubstantially constant. During this second phase of the refrigerationcycle, wherein expander piston 15 is moving downward and compressorpiston 16 is moving upward, refrigerant gas is transferred fromcompressor subchamber 13 to expander subchamber 12 through regenerator21. Regenerator 21 absorbs and temporarily stores heat from therefrigerant. In this way the temperature and pressure of the refrigerantis reduced.

When compessor piston 16 reaches the top of its stroke the third phaseof the refrigeration cycle begins wherein hydraulic pump P is operablyconnected to vent line V via hydraulic passages 50 and 49 to move valvespool 37 to the position wherein valve spool opening 40 is aligned withvalve port 42. The refrigerant gas pressure of the refrigerant gas inthe interconnected subchambers 12 and 13 then moves compressor piston 16downward to expell hydraulic fluid from reservoir 38 into vent line VDuring this third phase of the refrigeration cycle both pistons aremoving downward so that the total volume of the refrigerator chamber isincreasing. During this phase of the cycle the increasing volume withinthe chamber tends to decrease the refrigerant temperature. However, therefrigerant, at this time, absorbs heat from the walls of the housingthereby maintaining the refrigerant at a constant temperature which islower than the refrigerant temperature during the initial orfirstmentioned phase of the cycle. Thus, the thid phase is relativelyisothermal.

Expander piston 15 now completes its downward stroke and a fluid path iscompleted, via passages 43-48, between hydraulic pump P and vent line Vso that valve spool 31 is moved to bring valve spool opening 33 andvalve port 35 into alignment. Hydraulic pressure from hydraulic pump Pnow exerts a hydraulic force upon piston face 41 and expander piston 15begins its upward stroke. Thus the final or fourth phase of therefrigeration cycle is initiated. During this final phase pistons 15 and16 are again moving in opposite directions and preferably in such afashion as to maintain the volume of the refrigerator chamber constant.The upward traveling expander piston 15 now transfers refrigerant gasfrom expander subchamber 12 to compressor subchamber 13 throughregenerator 21. During this final phase the refrigerant gas obtains heatfrom regenerator 21 which was previously stored therein. Thus a completerefrigeration cycle has been generated. If the total volume of therefrigerator chamber has been maintained substantially constant duringthe second and final phases then a Stirling cycle will have beenapproximated.

Exemplarily, the refrigerant gas may be under a pressure in the rangeof, for example, from 100 p.s.i.g. to about 300 p.s.i.g. during therefrigeration cycle. The forces exerted upon displacers 27, 17, and 18and the force exerted on faces 41 and 42 respectively depends onpressure of the refrigerant gas or hydraulic fluid multiplied by thearea of the parts 27, 17, 18, 41 and 42. Pistons 15 and 16 may bereciprocated at any rate, as for example 2000 cycles per minute,depending on the cooling capacity desired. The motion of pistons 15 and16 may be sinusoidal or linear with time or otherwise. If it is desiredto approximate a Stirling cycle, the motion and size of the pistons, andother parameters should be selected to obtain substantially constantvolume conditions during the second and fourth phases of therefrigeration cycle.

The timing of the initiation of the compression strokes of pistons 15and 16 clearly depend on the manner in which the fluid passages arearranged. It should be equally clear that, by the provision of suitablemeans, such as apertured sleeves, circumscribing the portions of pistonscontaining passages 44, 47, 53 and 51, and rotatably positionedthereabout, either on the associated piston portion or on the associatedbore, the choice of a multiplicity of timing relationships is possible.

The cooling load may be maintained at cryogenic temperatures in a rangeof 20 Kelvin and higher. The cooling capacity of cryogenic refrigeratorcan be adjusted simply by throttling or changing the fluid pressure ofhydraulic pump P and P Rejection of heat through the walls of thehousing may be expedited by the provision of external means such as theforced conduction of air or liquid coolants and by the provision of heatradiating fins. The various hydraulic fluid passages may be arranged toobtain any desired synchronous phasing of the pistons and 16. Thus, itwill be appreciated that, while the described operation of the cryogenicrefrigerator generates the well-known Stirling cycle, it should bereadily apparent that other cycles may be generated with equal facility.

Various other modifications and improvements to the above-describedpreferred embodiment of the invention may be made within the skill ofthe art. Thus, if desired, the volume displaced by the moving pistons 15and 16 can be varied by changing the size of the displacers 27 and 18and corresponding subchambers 12 and 13. Regenerator means 21 need notbe carried by expander piston 15 and may be stationarily disposedadjacent piston portion 27. Also the embodiment may be modified by useof multiple stage regenerator means in lieu of the shown regeneratormeans. Where bellow fatigue is found to be a problem one may extend thewalls of the housing and provide additional piston heads to reducemechanical load thereon. An additional passage may be employed, asindicated by the dotted lines 58, interconnecting the bellow chamber 24to bellow chamber 56 to shunt a part of the refrigerant therethrough toreduce the mechanical load on bellows 19. Additionally, a plenum volume,as indicated by dotted lines 58a, in com munication with such passage58, may be provided to dampen pressure fluctuations in chambers 24 and56. Such damping naturally lessens the force contribution of refrigerantgas in bellows chamber 24 to the downward pushing of the piston 15during the previously described second phase of the refrigeration cycle.

Additionally, drive unit 28 can be readily modified so that hydraulicfluid may be utilized to drive pistons 15 and 16 in both directions ifbetter control of piston motion is deemed desirable. Thus, should springloads, insuflicient refrigerant gas pressure, or other factors, imposestrict design limitations to achieve the desired performance, additionalpiston faces, fluid passages, valve ports, and valve spool openings maybe provided to facilitate control of downward motion of pistons 15 and16. Exemplarily, the fluid required to drive the aforementionedadditional piston faces can be controlled by valve spools 31 and 37.

Accordingly, it should be understood that the invention as described isby way of illustration and not limitation and may be modified all withinthe scope of the appended claims.

What is claimed is:

1. In combination:

a plurality of fluid chargeable reservoirs each having fluid inlet andfluid outlet means;

a plurality of reciprocable elements each having a face positionedwithin a respective reservoir so that application of pressurized fluidthereto upon fluid charging of the respective reservoir is operative tomove the associated element;

valve means for allowing alternate fluid charging and discharging ofeach of said reservoirs via said fluid inlet and fluid outlet means by asource of pressurized fluid;

biasing means for urging and moving each of said elements upontermination of the application of pressurized fluid to the associatedface, said biasing means comprising an envelope defining an enclosedspace containing a pressurized medium arranged so that a movable part ofsaid envelope can exert a force upon each of said elements; and

element position sensing means associated with said elements forcontrolling the operation of said valve means to produce movement ofeach of said elements in timed relationship.

2. The combination set forth in claim 1 wherein said envelope ispartially defined by resilient means connected to each of said elements.

3. The combination of claim 2 wherein each of said resilient meanscomprises bellows.

4. The combination of claim 1 further comprising structure defining anenclosed space containing compressible refrigerant and also containingheat regenerator means and where said elements are arranged so thatmovement of said elements is operable to produce refrigeration.

5. The combination of claim 4 further including a cooling loadassociated with said structure.

6. The combination of claim 1 wherein said valve means comprises movablevalve spool means associated with each of said fluid inlet and fluidoutlet means.

7. The combination of claim 6 wherein each of said valve spool meanscomprises a member having fluid conducting means positionable bymovement of said valve spool means to allow the aforementioned alternatefluid charging and discharging of each of said reservoirs.

8. The combination of claim 6 wherein said sensing means includes fluidcontrol lines including fluid passages formed in said elements andarranged to operatively provide various fluid flow paths between saidvalve spool means and an external source of pressurized fluid so thatfluid flow through such paths is operative to move and position eachrespective valve spool means in a predetermined fashion.

9. The combination of claim 8 further including a refrigerating deviceand a cooling load associated therewith and wherein said fluid controlline means are interconnected so as to produce synchronous reciprocationof said elements and wherein said elements comprise part of said deviceso that reciprocation of said elements is operable to transfer heat awayfrom said cooling load.

10. In combination:

a plurality of fluid chargeable reservoirs each having fluid inlet andfluid outlet means;

a plurality of reciprocable elements each having a respective facepositioned within a respective reservoir;

means coupled to said reservoirs for supplying pressurized fluid theretoin order to charge said reservoirs;

valve means for allowing alternate fluid Charging and discharging ofeach reservoir;

said faces each being arranged so that application of pressurized fluidthereto upon fluid charging of the associated reservoir is operative tomove the associated element in a first direction;

means for urging and moving each of said elements in a second directionopposite to said first direction upon the termination of the applicationof pressurized fluid to the face of each element comprising an enclosedspace partially defined by respective parts of each element which spacecontains a pressurized medium which can exert a force upon each of saidparts to move the associated element in the second direction; and

element position sensing means associated with said elements forcontrolling the operation of said valve means to produce reciprocalmovement of each of said elements in timed relationship.

11. In a refrigerating system comprising a refrigerating device and afluid actuator therefor, the combination of: first and second chambers,a passage connecting said chambers, a regenerator associated with saidfirst chamber, and refrigerant gas in said chambers; third and fourthreservoir chambers each having an inlet and an outlet;

a first piston element arranged for reciprocation in said first andthird chambers;

a second piston element arranged for reciprocation in said second andfourth chambers;

said first piston including a first displacer arranged in said firstchamber and said second piston including a second displacer arranged insaid second chamber for displacing, compressing, and expanding saidrefrigerant gas, said pistons each being arranged for separatereciprocation in respective forward and re verse directions ofreciprocation;

first and second valve means respectively associated with said third andfourth chambers respectively for valve controlling the opening andclosing of said inlets and outlets whereby fluid under pressure may beallowed alternately to enter and exit the respective reservoir chambersto alternately move each ele ment in said forward direction ofreciprocation and enable each element to be moved in said reversedirection of reciprocation;

fluid actuator means operatively connected to both said valve means andcontrolled by said piston elements for effecting sequential opening andclosing of said inlets and outlets by said respective valve means insuch a way as to time the reciprocation of the respective elements; and

said refrigerant gas in said chambers being means for moving each saidelement in said opposite direction of reciprocation.

12. In a refrigeration system comprising a refrigerating device andfluid actuator therefor, the combination of:

first and second refrigerator chambers, a passage connecting saidchambers, refrigerant gas under compression in said chambers, and aregenerator arranged for storing heat absorbed from said refrigerant gasand for releasing the stored heat to the refrigerant gas;

a third reservoir chamber having an inlet and an outlet and a fourthreservoir chamber having an inlet and an outlet;

a first reciprocable piston element disposed for reciprocation in bothsaid first and third chambers and a second reciprocable piston elementdisposed for reciprocation in both said second and fourth chambers;

said piston elements each being further arranged to be separatelyreciprocable in respective forward and reverse directions so thatreciprocation of said elements in synchronous, out-of-phase relation iseffective to sequentially expand and compress said refrigerant gas whilesaid regenerator by absorbing and releasing heat as aforesaid eflectscooling in the vicinity of said first chamber;

supply means connected to each inlet for supplying fluid under pressureto each of said third and fourth chambers;

said piston elements being arranged so that fluid under pressure whensupplied to said third and fourth chambers respectively acts to driveeach piston element respectively in its forward direction by theexertion of fluid force against each piston element;

vent means connected to each outlet for venting the fluid from each ofsaid third and fourth chambers;

first and second valves each positionable in first and second positions,said first valve in its first position being operative to open saidinlet and in its second position being operative to open said outlet ofsaid third chamber, said second valve in its first position beingoperative to open said inlet and in its second position being operativeto open said outlet of said fourth chamber, the positioning of saidvalves effecting the supply and venting of the fluid to and from each ofsaid reservoir chambers by the opening and closing of said inlets andoutlets in a predetermined sequence;

valve actuator means for fiuidically positioning each of said valves bysequentially supplying fluid under pressure to each one or the other ofrespective valve actuator ports arranged on opposite sides of each ofthe respective valves;

fluid paths means communicating with said valve actuator ports fordefining a multiplicity of sequentially selectable fluid paths by whichfluid under pressure is conveyable via certain selected fluid paths tothe one or the other of said valve actuator ports on the opposite sidesof the respective valves to fiuidically move either of said valves fromeither one to the other one of its aforementioned first and secondpositions;

fluid path defining passages provided in said piston elements each beingalignable with said reservoir ports of the aforementioned fluid pathmeans upon reciprocation of said piston elements and being thusalignable during the reciprocation of said piston elements to effect theaforementioned sequential selection of certain ones of the aforesaidmultiplicity of fluid paths at certain times during such reciprocationin order to move each of said valves respectively at certain timesduring such reciprocation from either one to the other one of itsaforementioned first and second positions;

each piston element being arranged to further compress said refrigerantgas during movement in its forward direction which refrigerant gasdrives each piston element in its reverse direction by the exerofrefrigerant gas compression force against each piston element;

whereby reciprocation of said piston elements are driven as aforesaid bysaid fluid and pressure forces during the operation of the refrigeratingsystem.

13. In a refrigerating system including a refrigerating device and fluidactuator therfor, the combination comprising:

first and second interconected refrigerator chambers containingcompressible refrigerant under pressure therein;

third and fourth reservoir chambers for fluid each having an inlet andan outlet;

a first piston element extending between said first and third chambersincluding a first displacer disposed in said first chamber and a firstface disposed in said said third chamber;

a second piston element extending between said second and fourthchambers and including a second displacer disposed in said secondchamber and a second face disposed in said fourth chamber;

fluid supply means arranged for supplying fluid under pressure to eachof said third and fourth chambers via the inlets thereof, the fluidunder pressure being supplied to said third and fourth chambers in orderto push the faces of said pistons in order to move the associated pistonelement in a first direction of reciprocation; first and second valvesrespectively pistionable in either of two positions and each beingindependent of said piston elements, each valve being positionable toeither permit entry of fluid into different ones of said reservoirchambers via the inlets thereof or to permit the exhaust of such fluidfrom such chamber via the outlets thereof;

fluid control means for sequentially positioning said valves andcontrolled by the said piston elements in order to time thereciprocation of said piston elements, and

said valves and piston elements being arranged so that said refrigerantis operative to produce movement of each piston in a second direction ofreciprocation.

References Cited UNITED STATES PATENTS 321,085 6/1885 Carricaburu 91-193393,461 11/1888 Donald 91-193 2,274,224 2/ 1942 Vickers 91-191 2,698,5171/1955 Wilt 91-193 2,746,241 5/1956 Dros 60-24 3,045,436 7/ 1962 Gifford62-6 3,091,092 5/1963 Dros 62-6 3,119,237 1/1964 Gifford 62-6 3,188,8216/1965 Chellis 62-6 3,367,121 2/1968 Webb 62-6 35 WILLIAM J. WYE,Primary Examiner US. Cl. X.R.

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CER'lI. VIC/RTE O I" CORRECTION Patent No. 3,530,681 Dated September 29,1970 In n flab AXEL G-. DEHNE It is certified that: error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 1 line 16 delete the word "Continuation" and insert instead-Contamination.

Column 9 line 16 delete exer" and insert instead the word -exerti0n.

326N113 W2 a 11m (SEAL Amt:

mg I r mm 2. mm. m. Attestiflg 0mm Gomissioner of Patents

